Collagen matrices for use as an implant for repair of cartilage defects and injuries are known in the art. Of a particular interest is a honeycomb structure developed by Koken Company, Ltd., Tokyo, Japan, under the trade name Honeycomb Sponge, described in the Japanese patent JP3170693, hereby incorporated by reference. Other patents related to the current subject disclose collagen-based substrates for tissue engineering (U.S. Pat. No. 6,790,454) collagen/polysaccharide bi-layer matrix (U.S. Pat. No. 6,773,723), collagen/polysaccharide bi-layer matrix (U.S. Pat. No. 6,896,904), matrix for tissue engineering formed of hyaluronic acid and hydrolyzed collagen (U.S. Pat. No. 6,737,072), method for making a porous matrix particle (U.S. Pat. No. 5,629,191) method for making porous biodegradable polymers (U.S. Pat. No. 6,673,286), process for growing tissue in a macroporous polymer scaffold (U.S. Pat. No. 6,875,442), method for preserving porosity in porous materials (U.S. Pat. No. 4,522,753), method for preparation of collagen-glycosaminoglycan composite materials (U.S. Pat. No. 4,448,718), procedures for preparing composite materials from collagen and glycosaminoglycan (U.S. Pat. No. 4,350,629) and a crosslinked collagen-mucopolysaccharide composite materials (U.S. Pat. No. 4,280,954).
However, many of the above disclosed structures have uncontrolled parameters such as uneven and uncontrolled porosity, uneven density of pores, uneven sizes of the pores and random distribution of pores within the support matrix. Such uncontrolled parameters lead to usable pore structures that represent only a small percentage of the total implant. Additionally, when introduced into tissue defects or cartilage lesions during the surgery, these structures are difficult to handle as they are unstable and do not have appropriate wetting properties in that they can shrink or swell and are not easily manipulated by the surgeon.
For a tissue implant to be suitable for implantation, particularly for implantation into the cartilage lesion, the implant needs to be stable, easily manipulated, easily stored in sterile form and have a long shelf-life.
In order to provide a more uniform and sterically stable support structure for implantation into a tissue defect or cartilage lesion, inventors previously developed a collagen matrix having narrowly defined size and density of pores wherein the pores are uniformly distributed, vertically oriented and non-randomly organized. This matrix is disclosed in the co-pending patent application Ser. No. 11/523,833, filed on Sep. 19, 2006, hereby incorporated by reference in its entirety. Additionally, the acellular matrix suitable to be used as the primary scaffold is described in the priority application Ser. No. 10/882,581, filed on Jun. 30, 2004, issued as U.S. Pat. No. 7,217,294, on May 15, 2007, hereby incorporated in its entirety. However, even with the above-described improvements, a solution to problems faced by the surgeon during surgery is still lacking. A practicality needed for routine use of the tissue implants, such as, for example, the articular cartilage implants by the orthopedic surgeons, where the implant needs to be readily available, manipulatable, wettable, stable, sterile and able to be rapidly prepared and used for implantation, is still not achieved. All the previously described and prepared matrices or scaffolds require multiple steps before they are fully implantable.
Thus, it would be advantageous to have available an implant that would be easily manufactured and packaged, would be stable for extended shelf-life, would be easily manipulatable and rapidly wettable upon introduction into the lesion, could provide a support for cell migration or seeding and that could have, additionally, pre-incorporated drug or modulator in at least one portion of the implant. The implant should also allow the surgeon to introduce a drug or modulator during the surgical procedure.
It would also be an advantage to provide a secondary scaffold with an increased area of internal membranes which while not interfering with cell migration and nutrient exchange, nevertheless, would provide a substrate favorable to cell adhesion, growth and migration.
It is, therefore, a primary object of this invention to provide a method for treatment of tissue defects using a double-structured tissue implant comprising a primary scaffold and a secondary scaffold where each scaffold of the implant can assume a different function, be incorporated with cells, different drugs or modulators and/or be selectively chosen for performing a different function following the implantation.
The current invention provides such double-structured scaffold and a method for use for treatment of tissue defects by providing a first scaffold comprising a sterically stable and biocompatible support structure, preferably made of collagen, having defined pore sizes and density with said pores organized vertically and a second scaffold wherein said second scaffold is formed within said pores of said first scaffold. The double-structured scaffold of the invention is stable, resistant to shrinkage, swelling and dissolution, rapidly wettable, prepared in the sterile storageable form having a long-shelf life that can be easily surgically delivered and easily manipulated.
All patents, patent applications and publications cited herein are hereby incorporated by reference.